I understand that's where it originates, but it's still bad logic. The fact that the accused is guilty or is a total dirtbag doesn't preclude the victim from having been malicious or idiotic, and the victim's failings don't necessitate that we feel more sympathetic for the accused -- but rather that we feel less sympathetic for the victim. And that goes on the scale like anything else. There is a reason that self-defense is a defense to murder. The victim's actions matter.

The reason that "blaming the victim" is so offensive in the rape case, and why that is always brought out as the poster child for "don't blame the victim," is that in the rape case it implies that wearing a revealing outfit is enough to excuse rape. Which is so clearly, unquestionably wrong that it makes a very emotionally powerful case for the logically unsupportable position that the victim's actions never matter for anything.

But "don't [ever] blame the victim" is bad reasoning. To make it correct you would have to qualify it with something like "don't blame the victim when the victim isn't to blame" -- and that's just a tautology that doesn't help you determine when the victim is to blame. The fact that we know for sure that the victim isn't to blame in certain cases (e.g. rape) doesn't help for other cases where it isn't so clear.